Not all of Donald Trump’s excesses are unprecedented among U.S. presidents. Some are more extreme versions of pathologies that have appeared previously in U.S. politics and policymaking. Among these is a refusal to use the best sources of insight and information about the world beyond U.S. borders, and consequently the basing of foreign policy on inaccurate or distorted perceptions of that world.

The standard model of how senior policymakers acquire an understanding of situations overseas to which foreign policy is supposed to respond is that they get briefed by the national security bureaucracy, including the intelligence community, which in turn has a responsibility to tap the best available expertise both inside and outside government. But real policymaking does not follow the standard model. In a book I wrote several years ago about intelligence and U.S. foreign policy, I observed that intelligence has had little influence on the biggest departures in foreign policy, such as going to war or redirecting grand strategy. The images inside presidential heads that have shaped such departures have largely been ones that presidents brought with them upon entering office. Those images have had sources other than the bureaucracy, with some of those sources growing out of a shared American experience that has fostered certain distinctly American tendencies in looking at the rest of the world (the subject of a later book).

Other sources of presidential beliefs about the outside world are much narrower and more specific to the president involved. To the extent such narrowing excludes the insights of the best available expertise, this is bad and can lead to bad policy. Just how bad depends on exactly what those sources are. They can include the positive influence of a president’s own experience and intellect, which can lead to understanding of a foreign problem that is as insightful as anything the national security bureaucracy can furnish.

Richard Nixon, for example, had a jaundiced view of that bureaucracy. He disdained the “striped-pants faggots” in the State Department, and he forever resented the CIA for what he thought was its handling of the “missile gap” issue in a way that encouraged John Kennedy to exploit it successfully in the 1960 election campaign. One can identify subjects on which Nixon’s perceptions while president were less accurate than those of the bureaucracy he ignored—an example being his misinterpretation of India’s motives and objectives in the 1971 South Asia war. But overall, Nixon’s experience in previous public offices and his ruminations while out of power gave him a good understanding of how the world works, especially regarding great power relations, and that understanding undergirded his foreign policy successes.

Donald Trump disdains the national security bureaucracy at least as much as Nixon did, but he came into office with no alternative source of understanding about foreign relations. As the first U.S. president with no prior public service experience and one who doesn’t read books or most anything else, he probably has the shallowest understanding of world affairs of any president in U.S. history. A lack of appreciation of his own ignorance is suggested by his reply to a question about where he gets military advice: “I watch the shows.” The timing and substance of many Trumpian tweets demonstrate just how narrowly so many of his beliefs come from watching those shows, mostly on Fox News.

A further and more worrisome dimension to where Donald Trump acquires his beliefs is how he gets some of them from foreign sources with an agenda, including from the Russian government of Vladimir Putin. This pattern was established at the outset of Trump’s presidency with the Russian interference in the 2016 U.S. election, regarding which Trump has repeatedly shown more inclination to believe Putin’s denials than to acknowledge the evidence about the interference amassed by the intelligence community, special counsel Robert Mueller, and the press. More recently, the Russian leader has figured into the propagation of falsehoods regarding Ukraine. The several Ukraine-related canards that have floated into public discourse over the last few months evidently have various origins, not all of which are tied to the Russian government, but reporting by the Washington Post strongly suggests that Putin has been a critical influence in getting Trump to latch onto the falsehood that Ukraine had worked to defeat him in the 2016 election. It was after Trump’s private, unrecorded meetings with Putin at a G-20 summit in 2017 and the following year at Helsinki that Trump’s aides witnessed him pushing especially hard the notion that Ukraine and not Russia was the foreign regime that interfered in the U.S. election.

Two sets of harms flow from such foreign inculcation of a U.S. president’s misbelief. First, as with any other mistaken belief, it means that some U.S. policy is being shaped on the basis of misinformation. Second, a foreign regime has an opening to influence U.S. policy for that regime’s own ends. For both those reasons, the result is bad policy. Bad policy with an anti-Ukraine dimension surfaced again the other day with a White House threat to veto an omnibus spending bill. The threat led to stripping from the bill, in response to a demand from Trump, a provision that would have required the president to promptly dispense appropriated assistance funds for Ukraine, rather than being able to manipulate such assistance in the very manner that has already become grounds for Trump’s impeachment.

One can legitimately question what Donald Trump, in his most private thoughts, really believes about such things as Ukraine, Russia, and elections. His long record of chronic lying means that the falsehoods he pushes about Ukraine may be intentional lies every bit as much as many other lies he disseminates on countless other topics. But other dynamics inside Trump’s mind probably are involved. One is cognitive dissonance and the discomfort of any thought that his 2016 election victory was tainted by help from a foreign power. Trump would very much like to believe that Russian help did not make a difference in his win, and cognitive consistency leads him from that wish to a whole set of associated beliefs, including ones about Ukraine supposedly helping his opponent instead.

A related psychological dynamic is the tendency, among those who repeatedly propagate falsehoods that are related to objectives to which they are deeply committed, to begin to believe the falsehoods. Another factor is the replaying of canards by some in Congress and others in Trump’s camp, as part of an impeachment-obfuscation effort. The replays make it back to Trump, directly or via Fox. He can easily lose sight of how and why the mistaken notions began. The replays become further confirmation in his mind of beliefs that, however mistaken, he might genuinely hold.